Our invention relates to solid dielectric capacitors in general and, in particular, to ceramic capacitors such as those of the monolithic, multilayered configuration that are capable of sintering in a reductive or neutral atmosphere at sufficiently low temperatures to permit cosintering with base metal electrodes for the provision of low cost monolithic capacitors, and to a process for the fabrication of such low temperature sintered capacitors. The ceramic capacitors of our invention are particularly notable for their high DC breakdown voltages per unit thickness of the dielectric body.
Our invention may be considered an improvement of Japanese Laid Open Patent Application No. 59-138003. Described and claimed in in this prior patent application are dielectric ceramic compositions consisting essentially of a major proportion of {(Ba.sub.x Ca.sub.y Sr.sub.z)O}.sub.k (Ti.sub.n Zr.sub.1-n)O.sub.2 and a minor proportion of a mixture of lithium oxide (Li.sub.2 O) and at least one metal oxide (MO) selected from among barium oxide (BaO), calcium oxide (CaO) and strontium oxide (SrO). These ceramic compositions are sinterable to maturity in a reductive or neutral atmosphere. Thus, for the fabrication of monolithic, multilayered ceramic capacitors, for example, the prior art ceramic compositions make possible the costintering of dielectric ceramic bodies and film electrodes of nickel or like base metal interleaved therein.
The ceramic capacitors fabricated from these prior art materials have one weakness, however, particularly when they are used on motor vehicles. Capacitors for vehicular use must retain their full performance characteristics in a temperature range as wide as from -50.degree. to +125.degree. C. The direct current (DC) breakdown voltages of the capacitors in accordance with the prior art ceramic compositions are only from 13 to 18 volts for each micron of the thickness of the dielectric body at the maximum, 125.degree. C., of the expected working temperature range. A conventional solution to this low breakdown voltage problem has been to increase the total thickness of the dielectric body. Such greater size capacitors are of cource objectionable because of the larger space requirements.